1. Field of the Invention
The present invention relates to an inkjet recording apparatus and an ink cartridge.
2. Discussion of Related Art
There is known an inkjet recording apparatus which includes: an ink storage in the form of an ink cartridge removably installed in a main body of the apparatus; and a recording head held by the main body and operable to eject an ink, through a plurality of nozzle holes formed in the recording head, onto a recording medium supplied to the apparatus, so that a desired pattern of image is recorded on the recording medium. In such an inkjet recording apparatus, the nozzle holes are easily clogged with impurities such as thicken ink and bubbles generated in an ink passage communicating the ink cartridge and the recording head. There is also known a so-called “purging” operation which is carried out for removing the impurities from the nozzle holes.
There are proposed various methods for achieving the purging operation. For example, U.S. Pat. No. 4,558,326, which is incorporated by reference, in its entirety, or its corresponding JP-A-S59-59457 discloses an inkjet recording apparatus equipped with a purging system in which a cartridge case of an ink cartridge is provided by a rigid member and accommodates a flexible-material-made ink bag in its gas tight space while an air pump is operable to supply a positively pressurized air into the cartridge case so that the ink bag accommodated in the cartridge case is pressed by the positively pressurized air. An ink stored in the bag is forced to be supplied to a recording head under a high positive pressure, whereby impurities clogging the nozzle holes are removed from the nozzle holes.
In this inkjet recording apparatus disclosed in the above-indicated U.S. Patent, described more specifically, the ink cartridge is constructed to includes, in addition to the cartridge case and the ink bag, a spout cap which fluid-tightly plugs an opening of the ink bag and an opening of the cartridge case, and an elastic member which is fitted in a through-hole of the spout cap, for preventing outflow of the ink from the ink cartridge and inflow of a gas from the exterior of the ink cartridge, and also for receiving a hollow needle that is to be pierced through the elastic member. The cartridge case has another opening serving as an air conduction hole through which a positively pressurized air supplied from an air pump is introduced into the cartridge case.
When the ink cartridge constructed as described above is installed on a main body of the inkjet recording apparatus, the hollow needle is pierced through the elastic member, while the air pump is brought into communication with the air conduction hole through an air supply passage. During the recording operation, the ink stored in the ink bag is supplied to the recording head through the hollow needle, without the pressurized air being not supplied from the air pump. During the purging operation, the pressurized air is supplied from the air pump into the cartridge case through the air conduction hole, so that the ink stored in the ink bag is supplied to the recording head under a high positive pressure (see FIGS. 10 and 11 and columns 11–13 of U.S. Pat. No. 4,558,326).
In the inkjet recording apparatus as described above, however, it is necessary to gas-tightly seal not only the connection between the air conduction hole and the air supply passage but also the connection between the spout cap and the cartridge case, for avoiding leakage of the pressurized air from the cartridge case through these connections. Such a sealing arrangement inevitably increases a number of components of the apparatus and a number of steps in a process of manufacturing the apparatus, thereby increasing the cost of manufacture of the apparatus.
Further, since the opening of the cartridge case provided for fixing the spout cap to the cartridge case is gas-tightly sealed, the above-described another opening has to be formed in the cartridge case so as to serve as the air conduction hole. Therefore, an alignment of the air conduction hole with respect to the air supply passage is required in addition to an alignment of the elastic member (press-fitted in the spout cap) with respect to the hollow needle, thereby reducing a degree of freedom in designing the apparatus.
Further, the apparatus suffers from leakage of the ink in a periphery of the hollow needle (i.e., leakage of the ink through connection between the hollow needle and the elastic member), where the elastic member does not have a high degree of elasticity. This ink leakage is caused by a pressure difference between opposite sides of the elastic member. An inside surface of the elastic member (exposed to an interior of the ink bag) is subjected to the ink pressurized by the pressurized air, while an outside surface of the elastic member (exposed to an exterior of the ink bag) is subjected to the atmospheric pressure.